Common electronic devices include printed circuit to which electronic components serving as heat sources are mounted. One example of which is disclosed in Japanese Patent Application Publication No. 2014-13811.
Such an electronic device includes a printed circuit board to which such an electronic component is mounted, and a metallic housing in which the printed circuit board is installed. The printed circuit board is fastened to the housing with a screw while the screw serves as a heat dissipator for dissipating heat from the printed circuit board to the metallic housing. The electronic device is also configured to prevent disturbance noise from being transferred from the metallic housing to the printed circuit board via the screw.
Specifically, the printed circuit board is designed as a multilayer board comprised of separated conductor layers electrically isolated from each other. The conductor layers are fastened with the screw. The conductor layers include a metallic layer disposed at the inner side of the outermost layer thereof. The metallic layer extends from the lower side of the electronic component to the portion inside the multilayer board, which is pressed by the screw. The metallic layer is also electrically isolated from wiring patterns printed on the respective conductor layers.
The extension of the metallic layer up to the portion inside the multilayer board, which is pressed by the screw, increases the thermal contact conductance of the multilayer board through the metallic layer, resulting in an increase of the heat dissipation performance of the electronic device. The electrical insulation of the metallic layer from the wiring patterns prevents disturbance noise from being transferred from the metallic housing to the electronic element via the wiring patterns.